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When investigating potential causes of apparent declines in European brown trout angling catch rates over recent decades, fisheries management procedures are rarely considered. Using a 20‐year dataset of brown trout stocking and angling catch rates, we found a significant decline in brown trout angling catch rates in streams of East Bohemia, Czechia, were well predicted by a reduction in the number of brown trout stocked at catchable size (i.e. age‐3+). Increased stocking of smaller sized brown trout, and recent sporadic efforts to stock large brown trout, had no effect on catch rates. Our findings suggest that brown trout catch rates were related to 'put‐and‐take' stocking, in which non‐native rainbow trout gradually replaced brown trout in both stocking and catches. Our study stresses the importance of considering historical fisheries management, a sometimes‐neglected factor, when studying angling catches of economically important species. [ABSTRACT FROM AUTHOR]

Parasites of the invasive Chinese sleeper (Perccottus glenii) were studied in five different localities at the site of the first introduction of the Carpathian population of this fish. We recorded eight taxa of parasites in Lviv water bodies. The monogenean Gyrodactylus perccotti and the cestode Nippoteania perccotti were recorded in all five lakes studied. These parasites represent Far East species introduced together with their host. Also the copepod Neoergasilus japonicus is a Far East parasite introduced to Europe with its aquaculture vector. Differences between the surveyed bodies of water were mainly related to their local seasonal conditions and watershed characteristics. The current data confirm the presence of co-introduced populations of G. perccotti and N. perccotti, which probably affects the future invasiveness of their host. Due to low acquisition of local parasites, we cannot confirm any significant effect of invasive fish on local parasite assemblages in this region. However, the presence of the non-indigenous copepod, N. japonicus, requires additional attention in the future.

In recent years, pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) have spread intensively to many parts of Europe, including Ukraine. In this study, we (1) assess intra-population genetic variability in five widely-spaced Ukrainian pumpkinseed populations and compare their population genetic structure with other European populations and (2) provide a comprehensive survey of pumpkinseed parasites across the region. Discriminant analysis of principal components and FST analyses based on microsatellites indicated that all five populations formed discrete clusters. Within Europe, Ukrainian populations were most closely associated with populations from the River Danube, suggesting that the Danube is the main source of all Ukrainian pumpkinseed populations. The parasite fauna comprised 15 taxa, most of which (92%) were native to North America (monogenea Onchocleidus similis and O. dispar; myxozoan Myxobolus dechtiari). Parasites acquired in the species' new range occurred accidentally, with only Trichodina ciliates found relatively frequently and the eye flukes Diplostomum pseudospathaceum and Tylodelphys clavata occurring at higher prevalence. Absence of specific monogeneans in pumpkinseed from estuaries (Khadzhibey and Sukhyi Lymans) indicates low tolerance of Onchocleidus species to salinity.

The coexistence of sexual and asexual lineages is rarely documented in vertebrates. Various ecological and evolutionary mechanisms have been proposed to explain their stable coexistence. Gibel carp (Carassius gibelio), a highly invasive freshwater fish in Europe, is one such example of a sexual and asexual vertebrate, combining gynogenesis (sperm-dependent parthenogenesis) and sexual reproduction. In this study, we focused on vigour-related traits in gynogenetic and sexual forms of gibel carp coexisting in the same habitat, to reveal whether there is a link between parasite load and vigour-related traits reflecting the potential advantage of one reproductive form over another, which may eventually facilitate the obligatory coexistence of sperm-dependent gynogenetic females with sexual males. Using physiological parameters (indexes of somatic condition, energetic condition, and reproductive performance; glucose levels; and erythrocytes-related variables), diploid sexual males, diploid sexual females, and triploid gynogenetic females were found to be differentiated from one another. However, based on immune variables representing innate immunity, specific immunity, and index of immunocompetence, mostly sexual males were found to be weakly differentiated from both groups of females. We revealed different patterns of interactions between parasite abundance and immune variables between sexual and gynogenetic forms. Using parasite assemblage composition, different relationships between parasite assemblage and immunity or physiology in sexual males and sexual females were evidenced, potentially related to male reproduction biology. In contrast, gynogenetic females exhibited the advantage that parasite assemblage composition did not affect their immunity or physiology. Our study suggests that reproduction mode-associated costs of physiology and immunity may facilitate the coexistence of the asexual-sexual complex. We highlight that multiple ecological processes and evolutionary mechanisms contribute to the coexistence of asexual and sexual gibel carp. [ABSTRACT FROM AUTHOR]

Here, we present the results of a large-scale fish rescue prior to the building of flood protection structures along a stretch of the River Svratka running through Brno city centre (Moravia, Czech Republic). During this demanding and unique event, 5,861 fish, with a total weight of 1,951 kg, were caught and successfully transferred downstream. A total of 21 species of fish were recorded, of which two were protected species and two non-native to the Czech Republic. The dominant species caught (i.e. > 10%) were chub (Squalius cephalus), nase (Chondrostoma nasus), roach (Rutilus rutilus) and vimba bream (Vimba vimba), making up 85% of the catch. While this stretch of the Svratka supported a type-specific fish community dominated by rheophilic species, the occurrence of many species was supported through stocking by the Moravian Anglers Association. The length-frequency distribution of individual fish species suggests there has been a lack of recruitment over a relatively long period. This is most likely linked with hydropeaking from the Brno reservoir water power plant, with daily sharp fluctuations in flow in a river channel lacking shallow bankside areas and refuges with slowflowing water preventing fish fry survival. [ABSTRACT FROM AUTHOR]

In Poland, distribution of non‐native pumpkinseed Lepomis gibbosus (Centrarchidae) is strictly limited to the Oder river basin, where it was introduced in the early 20th century. Recently, several populations have been found in waterbodies adjacent to the Oder, particularly in its lower reaches. In this study, we compare the genetic relatedness of populations in the Oder basin with other European populations using nuclear (microsatellite) and mitochondrial (partial cytochrome c oxidase subunit I; cox1) markers. Microsatellite analysis indicated that four populations in the lower Oder form a separate cluster, while one in the middle Oder clustered with Danubian populations, from where probably having been introduced. Microsatellite data suggested that the lower Oder populations differ from other non‐native European populations, making it impossible to estimate the source of introduction. Nevertheless, analysis of cox1 indicated that Oder pumpkinseeds belong to the same haplotype as the vast majority of European populations. Parasitological examination confirmed the presence of two North American species, the monogenean Onchocleidus dispar and trematode Posthodiplostomum centrarchi, in the lower Oder, both previously unknown in the region. Fifteen other parasite species were acquired, including glochidia of invasive Sinanodonta woodiana. In the middle Oder, parasite infection was more limited. Fish from the Gryfino Canal, considered one of the most invasive populations in Europe, showed the highest parasite abundance and diversity, and the highest somatic condition and growth rate due to warm water released from the Dolna Odra power plant. Our results highlight significant differences in somatic condition and parasite infection in long‐established non‐native pumpkinseed populations in the same river system, reflecting mainly environmental conditions. [ABSTRACT FROM AUTHOR]

Round goby, Neogobius melanostomus (Pallas, 1814), an invasive Ponto-Caspian fish species, were registered in the upper Elbe for the first time in 2015, near the City of Ústí-nad-Labem (Czech Republic), apparently introduced by shipping. We sampled 53 individuals from this newly introduced population on May 18 (spring) and October 21 (autumn) 2016 in order to assess parasite load. Seven taxa were recorded, comprising two ciliates, one digenean (metacercariae), one acanthocephalan (cystacanth), two nematodes (larvae) and mollusc glochidia. No specific parasites were registered. Only the acanthocephalan Pomphorhynchus tereticollis was found in high numbers and occurred in both seasons, all other parasites occurring sporadically. Such a low parasite load is typical for Ponto-Caspian gobiids introduced far from their host range, and complies with the predictions of the ‘enemy release hypothesis’. All parasite species were probably acquired in the upper Elbe itself. According to the ‘parasite spillback’ concept, round goby could potentially play an important role in P. tereticollis distribution in the Elbe.

As invaders of European and North American aquatic systems, Ponto-Caspian gobiids are believed to represent a significant negative threat to native fish assemblages and cottid species in particular. To date, relatively few studies have tried to document actual impacts, most being short-term and/or laboratory based. Here, we examine 8 years (2008-2015) of electrofishing data from a 1200-m stretch of rip-rap along the Austrian Danube, initiated following establishment of four non-native gobiids: tubenose goby Proterorhinus semilunaris, bighead goby Ponticola kessleri, racer goby Babka gymnotrachelus and round goby Neogobius melanostomus. While we registered 26 fish species in total, most native species were caught along the rip-rap only occasionally. Only native bullhead Cottus gobio and the four non-native gobiids were caught regularly. Although cottids are presently believed to be most vulnerable to gobiid invasion, we observed no negative trend in bullhead abundance over the 8-year dataset, the population remaining stable and at similar abundances to gobiids. While we observed no significant trend in round, racer or tubenose goby abundance, bighead goby showed a continuous decline. Our data contradict previous reports of drastic impacts on cottid abundance by gobiids (mainly round goby), suggesting potential region-specific effects following invasion. [ABSTRACT FROM AUTHOR]

Antipredator strategies increase the chances of survival of prey species but are subject to trade-offs and always come at a cost, one specific category being the 'missed opportunity.' Some animals that can modulate the timing of life-cycle events can also desynchronize this timing with the occurrence of a predator. In an unpredictable environment, such a modification may result in a mismatch with prevailing conditions, consequently leading to reproductive failure. In eastern Africa, temporary pools existing only during the rainy season are inhabited by annual fish of the genus Nothobranchius. We examined (i) the capability of multiple Nothobranchius populations and species to cease hatching when exposed to chemical cues from native fish predators and adult conspecifics and (ii) the ability of N. furzeri to modulate their growth rate in the presence of a gape-limited fish predator. As the tested Nothobranchius spp. originate from regions with extreme environmental fluctuations where the cost of a missed opportunity can be serious, we predicted an inability to cease hatching as well as lack of growth acceleration as both the predator's gape limitation and the environment select for the same adaptation. Our results showed no biologically relevant influence of kairomone on hatching and no influence on growth rate. This suggests that, in an unpredictable environment, the costs of a missed opportunity are substantial enough to prevent the evolution of some antipredator defense strategies. [ABSTRACT FROM AUTHOR]